The influence of urea on actin-activated myosin Mg2+-ATPase of requiem shar
k Triakis scyllia was examined and compared to that of carp (Cyprinus carpi
o). No changes in the maximum turnover rate, V-max, was observed for shark
myosin up to 0.3 M urea which is an approximate physiological concentration
in marine elasmobranch tissues. The rate for carp myosin decreased by 70%
at this urea concentration. The affinity of myosin to actin also remained u
nchanged up to about 0.7 M urea for shark in marked contrast to carp myosin
which decreased by 30%, even in 0.1 M urea. Since it has been reported tha
t urea-resistibility of requiem shark myosin Ca2+-ATPase in the absence of
actin is comparable to that of carp, a high resistibility against urea in a
ctin-activated Mg2+-ATPase of shark myosin is partly accounted for by its s
table interaction with actin. (C) 1999 Elsevier Science Inc. All rights res
erved.